John Sawers, speaking in public for the first time since leaving the Secret Intelligence Service in November, said trust between governments and technology companies had been shattered and needed to be rebuilt.
"There needs to be some new compact between the technology companies and those who are responsible for security if we're not to see events like we saw in Paris last week ... becoming more and more features of our lives," Sawers said, also citing recent security incidents in Yemen and Nigeria.
Sawers blamed the breakdown in trust on revelations by Edward Snowden, the former US spy agency contractor who disclosed the extent of surveillance and electronic monitoring by the US and Britain. The debate Snowden had provoked over civil liberties was difficult, but not impossible, to resolve, Sawers said.
"I don't believe there is a trade-off between privacy and security; I think they go together," he said. "If you have a society which evades and abuses privacy, then ultimately there will be a reaction against the damage to your security."
National security is gaining political significance before Britain's elections in May and after attacks by Islamist gunmen in Paris that killed 17 people. Britain is on its second-highest threat level, meaning an attack is considered highly likely.
A "hardened core" of fighters returning to Britain from Iraq and Syria pose a real threat, Sawers said, and despite the efforts of security services and police an attack against the country will eventually happen.
Prime Minister David Cameron has promised laws giving greater access to online communication if he wins the May general election, but some of his rivals oppose the scale of his proposals.
Sawers backed Cameron's stance, saying that while he understood the value of online communication services like Facebook's WhatsApp and Apple's FaceTime, and used them himself, they could not be beyond the reach of monitoring agencies.
"If the technology companies allow to be developed areas which are simply impenetrable, you are inviting problems," he said at the release of a study by public affairs firm Edelman on attitudes towards bodies like the security services.
The call for greater monitoring of online communications is a familiar one from intelligence officials. On Sunday, a former head of the domestic intelligence service said Britain's anti-terror laws were "not designed for the current digital world" and no longer fit for purpose. — Reuters
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